When I try to add more than one Input/Output to a BPMN-Diagram, I can't see option to add it (i.e. 3 dots on the right-hand side).
The 'Input' and 'Output' attributes may not be defined as a Dictionary link (as a list).
Please check that the Custom attributes have been configured correctly.
The source of the 'Input' and 'Output' Dictionary items is usually from the original Trial Workspace creation, where the folder 'Process Example' has been provided.
Included with these examples are Dictionary items, such as the 'Input' and 'Output' attributes.
KBA , BPI-SIG-PM-DIC , Dictionary for SAP Signavio Process Manager , How To